When CPU at 100%, loss of ocl performance ?

I use ocl v1.00 and I noticed a huge loss of performance when my CPU is also busy.
Few figures :
- CPU 0% -> oclhashcat algo LM is at 800Mh/s
- CPU is at 100% -> oclhashcat algo LM is at 200Mh/s

What can explain this ?

Same behaviour with other algo (NTLM, WPA2, ..)

Thank you.
Propably because of host process can't load words from dictionary. You might want to retry with -a 3 and see if it still happens. If no, then that's the reason.
oclhashcat command line is already with -a (I do a digits only bruteforce on WPA) so no dictonnary needed).
With ocl-plus 0.15 it works ok but not anymore with v1.00.
Graphic card : MSI R7970 Twin Frozr 3GD5/OC BE 3 Go
Driver : 13-9_win7_win8_64_dd_ccc_whql
did a quick test... I used lookbusy to load CPUs to 95-99% (granted this is a synthetic load)

Cracking WPA2 with a really big wordlist.

WPA2 Before : 394 kH/s
under load : 384-390 kH/s everywhere in the range.

got 2 days left on this ruleset, then I can check NTLM.

3x ASUS HD7970
Driver Catalyst 13.11b (Suse 12.3)